1. Field of the Invention
This invention relates to new compositions comprising a mixture of a Novolak resin and a "resol" resin. More specifically, it relates to such mixtures in intimate, uniformly blended form which are capable, upon heating, of thermosetting and eventually, under appropriate carburizing conditions, of forming vitreous carbon.
2. State of the Prior Art
Vitreous carbon, as normally prepared, is at least 99.9% pure, having an ash content of 200 PPM or less. Thus, with its low permeability, negligible porosity and low specific surface, vitreous carbon carbon is very inert. Its resistance to hydrochloride, hydrofluoric, nitric, sulfuric and chromic acids and to mixtures of nitric acid with oxidizing agents is much better than with non-vitreous carbon. The rate of attack on vitreous carbon by molten zinc, lead, tin, phosphorus, silver, arsenic, etc., is very low.
The extreme inertness, impermeability and non-porosity qualifies vitreous carbon as an important and useful material of construction for use in a number of applications and in various industries. For research and development work this material has been used in fabricating beakers, basins, boats, reaction tubes, etc. and for extensive use in the processing of semiconductors, fluoride laser materials, zone refining of metals, zone refining of chemicals, biomedical applications, fuel cell electrodes, etc.
However, industrial applications of vitreous carbon have been made only in recent years. Since vitreous carbon is not wet by a wide range of metals including zinc, silver, copper, tin, lead, aluminum, gold, platinum and others, it has found application in the processing of some of these metals and their alloys, for example, in the dehydrogenation of molten aluminum with chlorine gas. Dip pipes of this material for corrosive liquids have also been successfully used.
The growth of industrial applications for this material has been restricted in large measure by the inability to produce large and properly cursed small moldings or extrusions in the required shapes and by use of conventional molds or dies at conventional rates and reasonable cost. There has been difficulty in making large thin plates suitable for use in fuel cells.
In the parent application, Ser. No. 397,497, the Patent and Trademark Office has relied on the following references: Redfern U.S. Pat. No. 3,109,712; Appleby et al U.S. Pat. No. 3,626,042; British Pat. Nos. 623,271, 1,020,441, 1,098,029 and 1,330,296; Japanese Pat. No. 54-20991; Grazen et al U.S. Pat. No. 3,879,338; Rice et al U.S. Pat. No. 3,927,140; and French Pat. No. 1,281,514. However, none of these references show the superiority of a phenol-furfuraldehyde Novolak in admixture with a phenol-formaldehyde resol for the preparation of vitreous carbon, particularly when there is a filler such as graphite in the mixture which makes it more urgent that the resin mixture has superior flow properties so as to avoid the strains and stresses that otherwise occur in the molded and vitreous carbon products. As pointed out hereinafter, the plasticity and flow properties contributed by the phenol-formaldehyde Novolak-phenol-aldehyde resol combination, particularly with a substantial amount of graphite filler, is not attainable by a phenol-formaldehyde Novolak combination with a phenol-aldehyde resol, nor by any such individual resin.